In recent years, in response to an ever-increasing speed in a wireless-data transmission, apparatuses utilizing a wireless LAN have been realized for practical use as an apparatus capable of ensuring a high-speed and stable transmission of image data, and the like.
Hereinafter is described a conventional wireless LAN apparatus. FIG. 34 is a block diagram illustrating the configuration of the conventional wireless LAN apparatus, which is disclosed in No. H11-239155 of the publication of unexamined patent applications. In the figure, a numeral 0101 denotes transmit data, which is input to a packet synthesizing unit 0102. The packet synthesizing unit 0102 sends the transmit data 0101 together with a buffer write signal 0104 to a buffer 103. A certain quantity of the data in the buffer 103 is read by a buffer read signal 0105 and sent to the packet synthesizing unit 0102. The packet synthesizing unit 0102 synthesizes the read data to there by create a transmit packet data 0106. The created transmit packet data 0106 is sent to a wireless transmit unit 0109 and transmitted as a wireless transmit signal via an antenna 0110.
The operation of the conventional wireless LAN apparatus configured in the foregoing manner is described referring to FIG. 35.
First, a packetization number in the packet synthesizing unit 0102 is set at “5”. The transmit data 0101 is now input per data block to the packet synthesizing unit 0102 at random times. The packet synthesizing unit 0102 writes the input transmit data 0101 together with the buffer write signal 0104 in the buffer 0103. When five data are stored in the buffer 0103, the packet synthesizing unit 0102 reads the data from the buffer 0103 for packetization and send the packet data to the wireless transmit unit 0109 as a transmit packet data 0106. These steps are repeated for data transmission.
However, in operating the conventional wireless LAN apparatus, a data volume for one packet is determined prior to the commencement of data communication between transmitting and receiving sides, while no particular change is made thereto in order to gain an optimum value after the communication commenced. Therefore, when a transmit rate in a wireless communication is changed, a packet length still remains the same.
In general, a communication rate in a wireless transmission channel is subject to changes according to a modulation system at a time of transmission. When the communication rate is high, an error rate is correspondingly high. The conventional method, however, does not allow the packet length to be extended despite the communication rate being low with fewer errors. Further, the packet length cannot be reduced either despite the communication rate being high with more errors. Thus, it is difficult to effectively use the transmission channel.
One of the measures to control errors when the transmission channel for wireless-communication is in bad shape is to reduce the packet length. The conventional method, however, does not allow the packet length to be changed, thereby making it impossible to select a suitable packet length depending on the status of transmission channel. Thus, the conventional method undergoes a load of errors resulting in quite a possible failure to maintain a required transmit rate.
Moreover, because the packet length cannot be changed in the conventional method when the input transmit data is temporarily slowed down, more time is required before the transmission. This is inadequate for the transmission of real-time data.
Also, it is necessary, in the conventional method, for the receiving side to prepare a receive buffer based on the assumption of a maximum rate and maximum packet length of the data to be received. This requires an excessively large buffer size creating another problem that the hardware increases.
The present invention is presented in light of the mentioned problems and designed to realize a constantly stable communication quality through an adaptive packet-length adjustment in response to changing conditions in connection with a wireless communication.